Methods and devices for reprocessing used PET bottles are known. In general, first the labels are released and removed. Then in another step, a mill is used to shred the bottles, including the caps, to form flakes. This product mixture is then washed in various washing steps and any glue residues are removed. Then the different types of plastic are separated (PET for the body of the bottle and polyethylene for the cap). In an optional subsequent decontamination step, the PET is then purified so that it can be reused to produce new bottles.
Examples of such reprocessing methods are described in U.S. Pat. No. 5,115,987 A, U.S. Pat. No. 5,688,693 A or German Patent 10 002 682 A1.
However, these known methods have the following disadvantage: in contrast with glass, where contaminants are deposited on the surface of the glass and can then easily be removed again, in the case of PET bottles, the contaminants diffuse into the material. Depending on how thick the walls of plastic are, the contaminants diffuse back out of the material at different rates in decontamination. To be sure that the shredded plastic material has in fact been completely purified, the reprocessing parameters must be adjusted so that even the most deeply contaminated components having thick walls must be adequately decontaminated. Therefore, in the state of the art, the cleaning and reprocessing parameters have been adapted to the thicker parts that are the most difficult to clean. However, this is economically feasible only to a limited extent because it involves “overcleaning” of the thinner plastic flakes.